Neither. Here is an idiom I occasionally use that does empty an array, though:

my $width = 4;
my @in = "a".."z";
while (my @row = splice(@in, 0, $width)) {
   print "@row\n";
}
__END__
Output:
a b c d
e f g h
i j k l
m n o p
q r s t
u v w x
y z
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